Method for manufacturing a light-alloy hybrid wheel including a front flange and a rim

ABSTRACT

A process for manufacturing a light-alloy hybrid wheel, implements the following separate operation phases: making a flange with an internal profile capable of constituting a tire bead seat; making a rim with, on one side, an outer profile capable of constituting a tire bead seat and, on the other side, a circular flank for assembly with a part of the flange; and assembling the flange with the rim, at the seat of said flange and the circular flank of the rim. The rim is made according to the following consecutive operations: an operation of manufacturing a circular flank; then an operation of expanding said circular flank to the size of the final rim in a single step; then an operation of cold or hot flospinning of said circular flank so as to obtain the rim in the final shape and profile thereof, comprising a shoulder only on the side that will not be welded to the flange.

The invention relates to the technical sector of wheels, particularlyfor vehicles, motor vehicles, and also to the foundry and forgingsectors for the manufacture of parts in light alloy, for example basedupon aluminum or magnesium, designed particularly for the automotiveindustry.

Known for example is the implementation of a wheel with a monoblock rimand flange obtained by molding, but requiring complex and costlytechnical means and recovering very substantial thickness dimensions,resulting in the weight of the wheel thus obtained being too great inrelation to current requirements.

In terms of the prior art according to FIG. 1, in relation to the twoaforementioned aspects, already known are hybrid wheels (R) in two partscomprising a rim (1) part and a front flange (2) or the wheel flange,these two parts being joined together by different connecting means.

One effective means was proposed for example in the patent EP 0 854 792which corresponds to a hybrid wheel in two parts which is obtainedaccording to a particular process. The connection between the rim andthe flange is provided by a weld obtained by means of a friction stirwelding operation. This technology, which is being exploited by one ofthe subsidiaries of the Applicant adequately responds to the demands ofthe market. However, the implementation of this process causes somedrawbacks in relation to new market requirements which are for exampleto obtain a reduction in the weight of products in the order of 20 to30% while maintaining a competitive price. Moreover, in the patent EP 0854 792, the wrought rim of the wheel is based on a centrifugally casttube that is transformed by lamination or by friction in order to obtainthe configuration of the final rim. These operations are long andcostly.

On the other hand, the Applicant makes use of a technology that combinesa foundry step and a forging step for aluminum alloy parts, known by thebrand name “COBAPRESS”. This technology is defined in the patent EP 119365 and consists in producing a foundry preform by casting of lightaluminum alloy, then in transferring the preform thus obtained to aforging die with significantly smaller dimensions than the dimensions ofthe preform to then perform a forging operation thus making it possibleto have the properties of the final part to be obtained. A deburringoperation is then performed on the edge of the final piece obtainedafter forging.

The applicant is already using this technology to produce wheels asdefined in patent FR 2 981 605, of which he is also the title holder. Inthis patent, the flange of the wheel is manufactured using COBAPRESStechnology that allows for a gain in weight. The flange is subjected toa forging step between two dies during this process. This forging stepis expensive, especially for small series wherein the manufacturing ofthese forging dies has a significant impact upon cost.

It is recalled that wheel rims must be arranged with profiles that actas seats (3) in order to support and restrain the beads of the tire (4).In order to obtain a reduction in this area, a recess was implemented bythe creation of a cavity (6) between the two welds (5) intended toconnect the rim part (1) to the flange part (2), (FIG. 5).

Other solutions have been proposed according to the prior art. Thus,from the point of view of the reduction in weight of the flange,different recess solutions for the tire bead seat have been described.

For example, in the patent EP 1230099, the title holder discloses asolution wherein one of the tire bead seats extends inward from theinner surface of the wall of the wheel rim such that it isself-supporting, while an outer profile of the wheel rim is not imposedby the inner profile of the wheel rim. This shape, which extends overthe entire circumference of the part, allows for a reduction in weightbut the drilling and positioning of the valve are difficult to implementwith this configuration.

The patent U.S. Pat. No. 5,271,663 describes another example embodiment,but using a different manufacturing technology. Recesses are made bymachining in low stress areas of the tire bead seat. These recessesallow for a reduction in weight as well as for balancing of the wheel.However, the machining of these recesses is a long and expensiveoperation.

Thus, according to the aforementioned prior art, existing solutions forthe implementation of recesses within the tire bead seat requiresignificant metal removal and are therefore costly and time-consuming.

The patent U.S. Pat. No. 6,536,111 describes another example embodimentof a hybrid wheel in two parts. The rim is made by the rolling of astrip of metal and then the welding end to end of both ends of thisstrip. The front flange is made by casting or forging, integratingrecesses in the tire bead seat. The rim and the front flange are thenassembled by welding, for example by electron beam, arc welding,friction or inertia. This second welding operation is performed on theoutside of the wheel which is then machined.

The approach of the Applicant was therefore, based upon the technologiescited above, to consider a design solution for a two-piece light-alloyhybrid wheel, improved in relation to known solutions and that wouldrespond to the needs of the market.

The applicant was therefore led to design and develop a new processbeginning with a specific selection of operational phases.

Thus, according to a first characteristic of the invention, themanufacturing process for a light-alloy hybrid wheel, particularly basedon aluminum or magnesium, including a front flange and a rim, implementsthe following different operational phases, according to which:

-   -   the flange is made with an internal profile capable of        constituting a tire bead seat;    -   the rim is made with, on one side, an external profile capable        of constituting a tire bead seat, and on the other side, a        circular flank for assembly with a part of the flange;    -   the flange is assembled to the rim, at the seat of said flange        and the circular flank of the rim.

The process is characterized in that the rim is made according to thefollowing consecutive operations:

-   -   an operation of manufacturing a circular flank; then    -   an operation of expanding said circular flank to the size of the        final rim in a single step; then    -   an operation of cold or hot flospinning of the circular flank so        as to obtain the rim in the final shape and profile thereof,        comprising a shoulder only on the side that will not be welded        to the flange.

In practice, during the manufacturing operation, the circular flank canbe obtained using any technique suitable for the intended application.

According to a preferred embodiment, the circular flank is made by hotor cold extrusion of a light alloy billet.

As an alternative, the circular flank is made by foundry casting.

As an alternative, the circular flank is made by powder sintering.

Other techniques can be implemented in order to manufacture the circularflank, without going beyond the scope of the invention.

Preferably, the expansion operation and flospinning operation arecold-made.

Advantageously, recesses are made in the seat of the flange, saidrecesses do not cover the circumference of the wheel, and have aU-shaped profile oriented in the direction of the rim assembly circulararea.

The flange can be made by casting, forging, or by a dual casting andforging operation.

According to a first embodiment, the dual casting and forging operationcomprises a casting operation of a foundry preform, a transfer of saidfoundry preform into a forging die, a forging operation of said foundrypreform in order to obtain the flask, and a deburring to obtain saidflask.

According to a second embodiment, the dual casting and forging operationcomprises a casting operation of a foundry perform, a storage of saidfoundry preform, a transfer of said foundry preform into an ovenallowing it to be heated, a transfer of said preform mold into a forgingdie, a forging operation of said foundry preform in order to obtain theflask, and a deburring to obtain said flask.

Preferably, when the flask is made by a dual casting and forgingoperation, the recesses are formed within the tire bead seat on theflask during the casting operation.

In a preferred embodiment, the assembly of the rim and the flange ismade by welding the circular flank of the rim and the flange by means ofa single friction stir weld using a pin, in a position that allowsaccess to both sides of the weld.

Friction welding using a pin is known as “Friction Stir Welding” or FSWin English. The welding is performed by mixing the material to a pastestate, i.e. to a solid phase. This technique makes it possible to weldalloys (such as aluminum) that are non-weldable or hardly weldable usingconventional techniques, involving the fusion of the material.Additionally, solid phase welding makes it possible to avoid theformation of bubbles that are likely to occur during a liquid-solidtransition. The material undergoes a smaller temperature increase, suchthat the thermally affected zone (TAZ) has better mechanical propertieswhen compared to conventional techniques. The strength of the weld understatic stress and fatigue is thus improved.

More preferably:

-   -   The friction stir welding is preceded by a machining operation        of assembly zones;    -   The friction stir welding is followed by a machining operation        on both sides (internal and external) of the weld in order to        remove burring and any eventual defects at the bottom of the        weld.

Alternatively, this assembly is made by other welding processescomprising a thermally affected zone.

For example, the weld may be obtained by laser or hybrid laser, byfriction stir welding between the two elements, or by means of CMT (ColdMetal Transfer) technology developed and patented by Fronius.

Regardless of the selected assembly mode, the wheel preferably has asingle weld, which is the one made between the flange and rim. Themethod thus offers many advantages, the expansion and flospinningoperations are particularly simplified compared to the patents FR 2 981605 and EP1230099B1 due to the use of a single weld instead of two.

As with the patents EN 2 981 605 and EP1230099B1, the wheel perfectlymeets manufacturer specifications in terms of impact resistance insofaras it has greater weight gain compared to traditional foundry madewheels.

Compared to the previously mentioned patent, the invention allows tosimplify the expansion operation which occurs in a single step insteadof two, and to simplify the flospinning operation because the geometricprofile of the final rim profile is much less complex due to the singleweld. It should also be noted that a single weld allows for a greatervariety of flange designs.

These and other characteristics will clearly emerge from the remainderof the description.

In order to associate the object of the illustrated invention in anon-limiting manner to the figures of the drawings,

FIG. 1 illustrates, according to the prior art, the implementation of ahybrid wheel in two parts with a rim part and a front flange part.

FIG. 2 illustrates the mounting of the tire on the rim with thepositioning of the tire beads on the seats thereof.

FIG. 3 schematically illustrates, according to the prior art, thesuccessive operations P1, P2, P3 in order to obtain the profile of therim.

FIG. 4 schematically illustrates according to the invention thesuccessive operations (obtaining a circular flank) P1, P2 (expansion ofsaid circular flank), P3 (circular flank flospinning operation in orderto obtain the profile of the rim).

FIG. 5 is a section view showing the profile of the rim according to theprior art, with a cavity formed on the rim.

FIG. 6 is a section view showing the profile of the rim according to theinvention with the implementation of a single weld and the formation ofrecesses within one of the tire bead seats.

FIG. 7 is a front view of the hybrid wheel with an illustration of therecesses.

In order to render the object of the invention more concrete, it isherein described in a non-limiting manner and illustrated in the figuresof the drawings.

As previously noted, the profile of the rim (1) is simplified by theexecution of a single weld (5) for the assembly thereof with the flange(2). The rim (1) has a circular profile (1 a) that acts as a seat forthe tire but only on the inside of the wheel. The other profile (2 a),acting as a seat for the tire, is implemented by the flange (2).

Hereinafter are highlighted certain features and advantages of theprocess of the invention.

FIGS. 3 and 4 illustrate the steps for obtaining the rim (1), accordingto the prior art and the invention respectively.

Within the scope of the invention, the rim (1) is made according to anoperation (P1) of the production of a blank in the form of circularflank (1 b); then an operation (P2) of expanding said circular flank (1b) to the dimensions of the final rim (1) in a single step; and finallyan operation (P3) of cold or hot flospinning the circular flank (1 b) soas to obtain the rim (1) in the final shape and profile thereof, withthe remaining part of the circular flank (1 b) on the side that will bewelded to the flange (2) and a shoulder (1 a) only on the side that willnot be welded to the flange (2).

According to one preferred embodiment of the manufacturing operation(P1), a light-alloy billet is made, this billet is then transformed intoa circular flank (1 b) by hot or cold extrusion. In comparison to otherknown techniques, this allows a flank to be obtained (1 b) that has verysignificant elongation. The flank expansion operation (1 b) can thus becold-made, i.e., at room temperature, which prevents warming before theexpansion thereof. In addition, this greater elongation makes itpossible to perform a cold flospinning operation (P3) after the coldexpansion (P2) operation. The material of the rim (1) is subjected tosignificant hardening during the cold flospinning operation (P3). Beforewelding the flange (2), the rim (1) is therefore subjected to heattreatment (for example T6: solution heat treating and aging), duringwhich the energy stored during the hardening is recuperated. This makesit possible to obtain fine recrystallized grains within the material ofthe rim (1). The microstructure thereof is therefore very fine and themechanical features of the rim (1) are improved in comparison to a hotconditioning technique.

In the P3 step, in FIG. 3, the profile is illustrated of the rim (1)which is required in order to obtain the cavity (6) illustrated in FIG.5 when the connection between the flange and rim is made using twowelds. The simplified rim profile (1) can be seen in the P3 step of FIG.4. This profile is in fact much simpler than that shown in the patent FR2 981 605, illustrated in the P3 step of FIG. 3. This simplification ismade possible due to the use of a single weld (5) implemented on thewheel of the invention. The external profile (1 a) of the rim (1) infact requires only one shoulder constituting a tire bead seat, insteadof two. The result is a gain in cycle time and a simplification to theflospinning machine, which reduces costs. The other profile (2 a),acting as a seat for the tire, is implemented by the flange (2).

Having a single weld (5) as shown in FIG. 6 also greatly simplifies thewelding operation in comparison to double welding. Indeed, the weldingis performed in one direction, perpendicular to the rim unlike thedouble welded wheel wherein the welds are in two different directions.It is no longer necessary to rotate the welding rod and the assembly issimplified and therefore less expensive, while there is a gain in cycletime and in the wear of the welding rod. The welding operation (5) isperformed at the junction of the part (2B) of the flange (2) and of thecircular flank (1 b) of the rim (1).

In addition, having a single weld (5) makes it possible to access bothsides of the weld. It is then possible to machine both sides of theweld. This machining which is commonly used with panels for aeronautics,makes it possible to remove any welding burrs and defects at the bottomof the weld that are often present with friction stir welding. Thesedefects correspond to bad mixing of the alloy which creates non-weldedseams at the bottom of the weld. The non-welded burrs or lips aredefects that lead to the onset of cracking when there is fatiguestressing of the wheel. The removal thereof is therefore a greatadvantage from the point of view of the reliability of the process.Access to both sides of the weld also makes it possible to perform afrequency penetration test on the weld in order to ensure the stabilityof the welding process and to ensure the absence of defects. For a wheelwith two welds, access to both sides of the weld is not assured. It istherefore necessary to section a wheel in order to perform thisfrequency test. In so far as this test is destructive, it results in theloss of part of the production and therefore an increase in costs forwheels with a closed cavity (6).

Laser and CMT welding, even though they are characterized by worsemechanical characteristics, may have an economic advantage. Indeed,laser welding can be competitive for very large runs and CMT weldingrequires a smaller investment. The mechanical characteristics of thesewelds are even better than those of MIG or TIG insofar as the thermallyaffected zone is reduced and fatigue resistance results are improved.They are still less resistant than FSW welds and requires more checkinginsofar as the welding is performed in the liquid phase. For the samemechanical performance of the part, a material thickness will berequired, which will result in the wheel being slightly overweight. Theuse thereof will therefore be reflected in terms of cost and increasedweight.

In a significant manner for the invention, the valve area is alsogreatly simplified. Indeed, for a wheel with two welds, the hole for thevalve leads to an opening in the cavity (6). The majority ofmanufacturers do not want to have cavities within the wheels insofar assaid opening leads to the possibility of the retention of water, gravelor other objects. A weld around the hole of the valve was thereforerequired in order to close the cavity (6) and to prevent waterretention. This weld therefore represented an addition to the processpresented in the patents FR 2981605 and EP 1230099, resulting in anadditional cost.

In addition, making the wheel in two parts before welding makes itpossible to implement more complex forms, that would not demoldable in asingle part wheel. This technology makes it possible to implementrecesses (7) at the flange (2), for example, in the form of cavities, ascan be seen in FIG. 7. These recesses are made either in a foundry, or aforge, or during the foundry step of the “COBAPRESS” process. They arelocated at one of the tire bead seats (3) that has the flange (2) andthat does not cover the circumference of the wheel. Indeed, these areas(8) are solid in order to increase the stiffness and resistance of thewheel. These solid areas (8) also greatly assist in fitting the tire.Indeed, without these solid areas the tire bead can be lodged within thecavities (7) during assembly. This tire bead can be difficult toposition within the seat thereof during assembly and having solid areascreates a slope which greatly assists in this operation.

An area is also left without a recess in order to allow for the drillingand the positioning of the valve with a simple geometry (9), as can beseen from FIG. 7. The recesses (7), as shown in FIGS. 6 and 7, have aweld (5) side U-shaped profile.

Making recesses is not new. In practice, the implementation of theserecesses during a forging or foundry step is economical insofar as itdoes not require a machining operation. This saves both cycle time andcost. The threshold value, i.e., the quantity of material involved withrespect to useful material, is also reduced.

In practice and according to the invention, this is remarkable due tothe combination of different phases of the process that on a practicallevel have a very large number of advantages over the prior art. It istherefore an optimization that has required significant research anddevelopment investments and that did not stem from the teaching of theprior art.

1. A manufacturing process for a light-alloy hybrid wheel including afront flange and a rim, the process implementing the following separateoperational phases: the flange is made with an internal profileconstituting a tire bead seat; the rim is made with, on one side, anexternal profile constituting a tire bead seat, and on an other side, acircular flank for assembly with a part of the flange; the flange isassembled to the rim, at the seat of said flange and the circular flankof the rim. wherein the rim is made according to the followingconsecutive operations: an operation of manufacturing the circularflank; an operation of expanding said circular flank to a size of thefinal rim in a single step; an operation of cold or hot flospinning ofthe circular flank so as to obtain the rim in a final shape and profilethereof, comprising a shoulder only on a side that will not be welded tothe flange.
 2. The manufacturing process according to claim 1, wherein,in the manufacturing operation, the circular flank is made by hot orcold extrusion of a light alloy billet.
 3. The manufacturing processaccording to claim 1, wherein, in the manufacturing operation, thecircular flank is made by casting in a foundry.
 4. The manufacturingprocess according to claim 1, wherein, in the manufacturing operation,the circular flank is made by powder sintering.
 5. The manufacturingprocess according to claim 1, wherein the expansion operation andflospinning operation are cold-made.
 6. The manufacturing processaccording to claim 1, wherein recesses are made in the seat of theflange, said recesses do not cover a circumference of the wheel, andhave a U-shaped profile oriented in a direction of the circular flank ofthe rim.
 7. The manufacturing process according to claim 1, wherein theflange is made by casting.
 8. The manufacturing process according toclaim 1, wherein the flange is made by forging.
 9. The manufacturingprocess according to claim 14, wherein the flange is made by a dualcasting and forging operation.
 10. The manufacturing process accordingto claim 9, wherein the dual casting and forging operation comprises acasting operation of a foundry preform, a transfer of said foundrypreform into a forging die, a forging operation of said foundry preformin order to obtaining the flask, and a deburring to obtain said flask.11. The manufacturing process according to claim 9, wherein the dualcasting and forging operation comprises a casting operation of a foundrypreform, a storage of said foundry preform, a transfer of said foundrypreform into an oven allowing the foundry preform to be heated, atransfer of said foundry preform into a forging die, a forging operationof said foundry preform in order to obtain the flask, and a deburring toobtain said flask.
 12. The manufacturing process according to claim 6,wherein the flask is made by a dual casting and forging operation, andthe recesses are formed within the tire bead seat on the flask duringthe casting operation.
 13. The manufacturing process according to claim1, wherein assembly of the rim and the flange is made by welding thecircular flank of the rim and the flange by a single friction stir weldusing a pin, in a position that allows access to both sides of the weld.14. The manufacturing process according to claim 13 wherein the weldingby a single friction stir weld is preceded by a machining operation ofassembly zones.
 15. The manufacturing process according to claim 13,wherein the welding by a single friction stir weld is followed by amachining operation on both sides of the weld in order to remove burringand any eventual defects at a bottom of the weld.
 16. The manufacturingprocess according to claim 1, wherein assembly between the rim and theflange is made by a weld obtained by CMT (Cold Metal Transfer)technology.
 17. The manufacturing process according to claim 1, whereinassembly between the rim and the flange is made by a weld obtained bylaser or hybrid laser.
 18. The manufacturing process according to claim1, wherein assembly between the rim and the flange is made by a weldobtained by friction stir welding with cyclical movement between the rimand the flange.